The present invention relates to an interface circuit, a power converter using the same and an electric vehicle using the same, particularly to an interface circuit preferably used to control a power transistor, a power converter using the same, and an electric vehicle using the same.
In a conventional motor load drive system, an interface circuit comprising a photo-coupler is arranged between the control unit as a circuit for a control system and a power semiconductor. To put it another way, since the power semiconductor for driving the motor as a load causes large current to be switched in a short time, the voltage occurring to stray inductance changes the potential of the ground of a large-current circuit, with the result that noise is produced. Accordingly, wiring for large-current circuit ground and that for small-signal circuit ground are provided. To avoid an operation error caused by noise due to stray inductance, control signals are transferred from the small-signal circuit to the large-current circuit through a photo-coupler, thereby allowing the small-signal circuit and large-current circuit to be separated electrically.
Patent Document as a prior art stated as above may be cited as follows, for example;
Japanese Application Patent Laid-Open Publication No. 2001-327171
However, since the photo-coupler uses an optical device, there has been a problem of low durability and hence poor reliability. Especially in an electric vehicle where wheels are driven by a motor, even though the working temperature environment is found in such a wide range as −40 through +105 degrees Celsius, the usable temperature range of the photo-coupler is smaller than that, and durability is much reduced in low or high temperature. When the photo-coupler has broken and control signals cannot be transferred to the large-current circuit from the small-signal circuit, the motor control will be disabled and the electric vehicle cannot be driven any more, with the result that reliability for control is reduced.
On the other hand, if the power converter is not used, control signals cannot be supplied correctly to the power transistor due to noise caused by the aforementioned stray inductance.
The object of the present invention is to provide an interface circuit characterized by improved control reliability without a photo-coupler, a power converter using the same, and an electric vehicle using the same.